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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tycho Andersen <tycho@tycho.ws>,
        Tejun Heo <tj@kernel.org>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.5 068/170] cgroup1: dont call release_agent when it is ""
Date:   Tue, 31 Mar 2020 10:58:02 +0200
Message-Id: <20200331085431.650236415@linuxfoundation.org>
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From: Tycho Andersen <tycho@tycho.ws>

[ Upstream commit 2e5383d7904e60529136727e49629a82058a5607 ]

Older (and maybe current) versions of systemd set release_agent to "" when
shutting down, but do not set notify_on_release to 0.

Since 64e90a8acb85 ("Introduce STATIC_USERMODEHELPER to mediate
call_usermodehelper()"), we filter out such calls when the user mode helper
path is "". However, when used in conjunction with an actual (i.e. non "")
STATIC_USERMODEHELPER, the path is never "", so the real usermode helper
will be called with argv[0] == "".

Let's avoid this by not invoking the release_agent when it is "".

Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/cgroup/cgroup-v1.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 84bedb87ae137..a1fbf500d0af7 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -785,7 +785,7 @@ void cgroup1_release_agent(struct work_struct *work)
 
 	pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
 	agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL);
-	if (!pathbuf || !agentbuf)
+	if (!pathbuf || !agentbuf || !strlen(agentbuf))
 		goto out;
 
 	spin_lock_irq(&css_set_lock);
-- 
2.20.1